The present invention relates to magnetic recording apparatuses having high performance and high reliability, magnetic recording media for realizing the apparatuses and methods for fabricating the same.
With recent remarkable development of a high information-oriented society, multi-media which combine information of various forms are rapidly spread. One of the information recording apparatuses which support the rapid spread of multi-media includes magnetic recording apparatuses such as magnetic recording disks. At present, improvement in recording density and miniaturization are attempted for magnetic recording disks. Furthermore, reduction in price of magnetic recording disks is being rapidly forwarded.
For realization of high density magnetic recording of magnetic recording disks, the following are essential techniques: (1) reduction of the spacing between the magnetic recording disk and a magnetic head, (2) increase of coercivity of the magnetic recording disks, and (3) new devising of signal processing method.
Among them, as for the magnetic recording disks, in order to realize a recording density exceeding 10 Gb/in2, it is necessary to reduce the switching volume of magnetic layer occurs as well as to increase the coercivity. For this purpose, magnetic grains constituting the magnetic layer must be fine in their size. Furthermore, in addition to the reduction of size of the magnetic grains, uniformity in distribution of the size is important from the viewpoint of thermal fluctuation. For the control of the size of magnetic grains in the magnetic layer and the distribution of the size, U.S. Pat. No. 4,652,499 proposes to provide a seed thin layer under the magnetic layer.
However, in the conventional method, there is a limit in control of crystal grain size and distribution of the crystal grain size of the magnetic layer constituting the magnetic recording disk, and fine grains and coarse grains coexist in the magnetic layer. In the case of recording an information (in the case of magnetic inversion), the magnetic layer in this state sometimes cannot attain stable recording when ultrahigh density recording higher than 10 Gb/in2 is carried out because of the influence of leakage field from the surrounding magnetic grains or the interaction with the large magnetic grains.
Accordingly, the first object of the present invention is to provide a magnetic recording medium of high performance and low noise by making finer the size of magnetic grains in the magnetic layer. The second object of the present invention is to provide a magnetic recording medium of low noise, low thermal fluctuation and low thermal decay by controlling the distribution of the magnetic grain size to become uniform. The third object of the present invention is to provide a magnetic recording medium suitable for high density magnetic recording by controlling the crystalographic orientation of the magnetic layer. The fourth object of the present invention is to provide a magnetic recording medium reduced in magnetic inversion unit at the time of recording or erasion by reducing magnetic interaction between magnetic grains. The fifth object of the present invention is to provide a magnetic recording medium capable of performing an ultra-high density magnetic recording of higher than 10 Gb/in2.
The above objects can be attained by a magnetic recording medium comprising a non-magnetic substrate, an inorganic compound layer which is formed on the substrate and which contains a crystalline first oxide (which is in the form of crystal grains according to X-ray diffraction) comprising at least one oxide selected from cobalt oxide, chromium oxide, iron oxide and nickel oxide and a second oxide comprising at least one oxide selected from silicon oxide, aluminum oxide, titanium oxide, tantalum oxide and zinc oxide, said second oxide being present at grain boundary of crystal grains of said first oxide, and a magnetic layer formed on said inorganic compound layer.
Moreover, the inorganic compound layer preferably has such a structure that the crystal grains of the first oxide have a hexagonal honeycomb structure, the grains are two-dimensionally regularly arranged, and the second oxide is present as amorphous substance (measured to be amorphous according to X-ray diffraction) at the crystal grain boundary of the first oxide. The crystal grains of the first oxide are made fine, and distribution of the size is nearly uniform. The crystal grains are most preferably crystallographically oriented.
Orientation, crystal grain size and distribution of the crystal grain size of the inorganic compound layer can be controlled by optionally selecting the constituent material and the concentration (composition) of the first oxide and the second oxide or the conditions for the formation of the layer.
The inorganic compound layer formed on the substrate is preferably of prismatic texture in which the crystal grains of the first oxide grow in thickness direction of the layer. In this case, thickness of the layer is preferably about 10-100 nm.
Furthermore, the inorganic compound layer made in platy form can be used as a substrate. In this case, the crystal grains of the first oxide preferably have a prismatic texture in thickness direction.
When the magnetic layer is formed on the inorganic compound layer, the magnetic layer is epitaxially grown from the crystal grains in the inorganic compound layer. Since the amorphous second oxide is precipitated at the grain boundary of the crystal grains in the inorganic compound layer, the magnetic layer epitaxially grows on the crystal grains and does not epitaxially grow on the amorphous portion. Thus, the growing state of the magnetic layer on the crystal grains differs from that on the amorphous crystal grain boundary in the inorganic compound layer, resulting in variation of orientation or texture of the magnetic layer. This variation causes variation of magnetic properties, and the magnetic interaction between the crystal grains constituting the magnetic layer can be diminished.
Furthermore, the spacing between the crystal grains in the inorganic compound layer can also be easily controlled by controlling the composition of the compound. The magnetic interaction between the magnetic crystal grains can be diminished by the control of the spacing.
By diminishing the magnetic interaction between the crystal grains constituting the magnetic layer, a zigzag pattern present in the magnetic transition area can be made smaller. Specifically, width of the zigzag pattern present in the magnetic transition area of the track of the magnetic recording medium can be made less than the gap length of a recording head. The width of the zigzag pattern may not necessarily be smaller than the gap length along the whole track, but it is ideal that the width is smaller than the gap length along the whole track. The relation between the width of the zigzag pattern and the gap length in this case is shown in FIG. 9. In this way, noise of the magnetic recording media can be reduced. Furthermore, since influence of noise can be made small even when the width of the track is reduced, track density can be lowered.
In order to perform smooth epitaxial growth, it is preferred that the crystal structure of the crystal grains in the inorganic compound layer is the same as or similar to the structure of the magnetic grains constituting the magnetic layer. The term xe2x80x9csimilar toxe2x80x9d here means that the difference of lattice constant of the crystal grains in the inorganic compound layer from that of the magnetic grains constituting the magnetic layer is within the range of xc2x110%. However, when the difference of lattice constant of the crystal grains in the inorganic compound layer from that of the magnetic grains constituting the magnetic layer is outside the range of xc2x110%, a layer having a lattice constant which is middle between both the lattice constants can be provided between the two layers.
When the magnetic layer is epitaxially grown from the inorganic compound layer as mentioned above, form and size of crystal grains in the inorganic compound layer become nearly the same as those in the magnetic layer. That is, the size of crystal grains in the magnetic layer is determined by the size of crystal grains in the inorganic compound layer. Therefore, the crystal grains of the magnetic layer become fine and distribution of the size becomes uniform. Specifically, the average grain size of the crystal grains of the magnetic layer is preferably 10 nm or less, and the distribution of the grain size is preferably 2 nm or less in terms of standard deviation "sgr".
Furthermore, the crystal grains in the inorganic compound layer are made fine and the distribution of the size is uniform, and the grains are regularly arranged. Therefore, the crystal grains of the magnetic layer formed thereon also become fine, and the distribution of the size is uniform and can be controlled so that the grains are regularly arranged. Accordingly, noise, thermal fluctuation and thermal decay caused by the magnetic recording media can be diminished.
By the above-mentioned techniques, magnetic inversion unit and size thereof in magnetic recording media can be made small. The magnetic inversion unit here is defined as follows. The minimum unit of inversion is assumed to be one crystal grain of the magnetic layer, and the number of units corresponding to the number of the crystal grains of the magnetic layer when recording or erasion is carried out is determined by observation with a magnetic force microscope (MFM) or the like.
Here, it is preferred to use, as the magnetic layer, a ferromagnetic thin layer of an alloy mainly composed of Co and additionally containing Pt and at least one element selected from Cr, Ta and Nb. Furthermore, in the structure of this ferromagnetic thin layer, at least one element selected from Cr, Ta and Nb is present in the form of segregation at the grain boundary of Co crystal grains.
Moreover, there is provided a magnetic recording apparatus comprising the magnetic recording medium, a driving part which rotates the magnetic recording medium, a recording head comprising a recording part and a read back part, and a means of moving the recording head relative to the magnetic recording medium. Thus, a magnetic recording apparatus can be realized which can perform high density magnetic recording of higher than 10 Gb/in2, furthermore, higher than 20 Gb/in2. In addition, various information such as images, code data and audios are recorded in this apparatus or read back from this apparatus, or the information is erased.